Olympic track star Oscar Pistorius is expected to take the stand next week in South African court to explain his side of what happened the night he shot and killed his girlfriend Reeva Steenkamp.

Prosecutors have built a good case against Pistorius, but he still has a chance of being found not guilty of murder, South African defense attorney and former state prosecutor Marius du Toit told Business Insider.

If he's found not guilty of murder, he could get convicted on a lesser charge of culpable homicide, meaning he acted in what he thought was self-defense, but was still negligent in shooting Steenkamp.

Pistorius claims he fired four shots through a locked bathroom door at his Pretoria house on Feb. 14, 2013 because he thought Steenkamp was an intruder. He says he woke up and heard a noise in the bathroom, remembered there were no bars on the bathroom windows, and thought contractors working on the property had left ladders outside. Pistorius says he assumed Steenkamp was still in bed next to him.

"Everybody knows there wasn't at any stage a burglar," says du Toit, the South African lawyer. "What he has to show is that in his mind, that was his belief and it was a reasonable belief."

Prosecutors still have compelling evidence that refutes Pistorius' story, including testimony from neighbors who said they heard arguing and a woman screaming at Pistorius' house the night Steenkamp died.

A ballistics expert also testified that the first two shots did not kill Steenkamp, so she would have had time to yell out before the fatal shot was fired.

AP

Another piece of evidence bolstering the prosecution's case is a text conversation between Pistorius and Steenkamp from just weeks before she died in which she tells Pistorius she's "scared of [him] sometimes."

Du Toit said the state has "really done well" so far in its case, but Pistorius could still be found not guilty of the most serious charge against him because the burden is on the prosecution to prove he meant to kill Steenkamp.

"Oscar's version [of what happened] only has to be reasonably possible," he said. "The scale is always tipped in the favor of the accused."

"If it's a reasonable possibility that [his version of events] could have taken place, the court has to give him the benefit of the doubt," du Toit said. However, he added, "I think he's got a lot to do in order to [prove that]."

If the court accepts his story as plausible, he's still likely to be convicted of culpable homicide, which leaves the penalty up to the judge. (Premeditated murder, on the other hand, comes with a minimum 25-year prison sentence.)

On Pistorius' side is the violent environment in South Africa.

Many South Africans have trained themselves to be constantly wary of safety risks within their own home. Many middle-class houses are surrounded by 10-foot walls and come equipped with "rape doors" to keep intruders out of bedrooms, Toronto Star sports columnist Cathal Kelly wrote in an editorial last year.

But still, the question remains as to whether Pistorius had the right to fire four shots through a locked bathroom door, even if he did think there might be an intruder inside.

A Cape Town criminal lawyer told the New York Daily News: "Oscar admits to shooting four shots through a closed door that led into a very small area, the toilet. ... The legal question is: Can you shoot four shots in those circumstances? Even if you think there is an intruder in your house ... where there is no imminent danger, you can't."